Method of and apparatus for radiosignaling.



H. SHOEMAKER.

METHOD OF AND APPARATUS FOR RADIOSIGNALING. APPLICATION FILED OCT. 4, I9I3.

1 ,241,565. Patented Oct. 2, 1917.

x Snwwlioz 77l- G b n l .4 $5 emom M.

UNITED STATES PATENT OFFICE.

HARRY SHOEMAKEB, OI JERSEY CITY, NEW JERSEY, ASSIGNOR TO MARCONI WIRE- LESS TELEGRAPH COMPANY OF AMERICA, OF NEW YORK, N. Y., A. CORPORATION OF NEW JERSEY.

Specification of Letters Patent.

Patented Oct. 2, 1917.

Application filed October 4. 1918. Serial No. 798,278.

To all whom it may concern:

Be it known that I, a citizen of the United States, residing in Jersey City, county of Hudson, State of New Jersey, have invented or discovered certain new and useful Improvements in Methods of and Apparatus for Radiosignaling, of which the following is a full, clear, and complete disclosure.

My invention relates to methods of and apparatus for transmitting and receivin either damped or undampe oscillations an particularly to methods and systems in which teliephones are employed for receiving signa s.

It is well known that the ordinary radiotelegraph receivers using telephones for receivmg signals will not work with continuous or undam ped oscillations unless the transmitting circuits or receiving oscillation circuits are interrupted. This is due to the fact that undamped oscillations pro duce a substantially continuous unidirectional flow in the telephone circuit. It is also well known that when damped oscillations are used, the telephone diaphragm will not res 0nd if the spark frequency is too high. t is also well known that with damped oscillations the energy which can be transmitted from the sending to the re ceiving station is proportional to the spark frequency or the num er of wave trams per second, and that it is advantageous to in crease the number of wave trains radiated from a transmitting station provided a receiver is used which will act quantitatively or have its action increased by the amount of received energy. In this connection it is known that when any of the well known crystal, electrolytic or rectifying detectors are used in conjunction with a galvanometer the alvanometer reading will be approximate y proportional to the spark frequency when damped oscillations are used, provide however, that the energy or amplitude of the wave trains is constant. For instance, if there be one thousand wave trainsper see ond the galvanometer will show up roximately one-half the energy received t at it would if there were two, thousand wave trains per second. On the other hand, ,it

HARRY SHOEMAKER,

trains per second than with one thousand wave trains per second, and that the loudness of the signal depends on the amount of energy contained in each wave train. It has also been observed that, in the case of signals received by means of a telephone, signals having certain wave train frequencies are more easily read than others having different fre uencies, and that this is especially true i the telephone receiver is subjected to sinusoidal electromotive force. The following table shows the voltage necessary to ive audible signals with different frequencies, and was compiled by Dr. Austin of the Bureau of Standards from tests on a certain make of telephones:

pair of Schmidt- Wilkes 800-ohm Volt sensit'ioeness of a telephones.

Volts to prod uce .Millionth:

nfe volt.

From the above table it will be seen that with a sinusoidal electromotive force, the telephone gave an audible signal with .0000006 volt at a frequency of 900., while with the lower frequencies it required. a much higher voltage. If, however, the electromotive force is not sinusoidal, as is the case in wireless telegraph receivers, as heretofore constructed, there will notbe much increase in sensitiveness with an increase of frequency. The electromotive force to which the telephones are subjected in radiotelegraph receivers heretofore used is in the natureof very short impulses, with considerable time intervals between such impulses. Therefore there cannot be much building up or increase in the strength of signals due to resonance even if the circuits are properly adjusted. Resonance in this case is meant to indicate coincidence between the frequency of the applied E. M. F. and the natural period of the telephone diaphragm. From the foregoing it will be seen that the use of telephones for receiving signals in either damgied or undamped wave systems has hereto ore involved certain limitations and objectionable features and it is the object of my inventionto overcome theseand to produce new and improved receiving paratus which will be more reliable and ei cient than that heretofore used.

My invention is based on certain observations and discoveries which, briefly stated, are as follows:

I have discovered that its small alternating current generator having a speed adapted to produce alternations of a frequency best adapted to operate a telephone dia= phragm, say, 900 cycles, beinserted between the rectifying device of a receiving system and the telephone, and so connected that the rectified energy will pass through its fields while the current from its armature will pass through the telephone, the telephone will be subjected to a sinusoidal electromotive force which will be substantially proportional to the current flowing through the fields, which in turn will be proportional to the received energy or the number of wave trains received per second. I have further discovered that by inserting in series with the armature and telephone a condenser of proper value, the reactance of the armature and telephone circuit may be given a zero value and the reaction on the field minimized, thereby materially improving the operation of the system. I have further discovered that by shunting the fields of the generator with a condenser of proper value the current flow through the fields can be made approximately constant when the energy iseither in the form of undamped waves or waves having a high spark frequency. With either form of waves the strength of the signals will depend on the amplitude of the received waves, while the note of the telephone will depend on the number of poles in the generator and the speed of the armature.

With the foregoing preliminary explanation in mind, my invention will be readily understood from a description of the arran ement and method of operation of the pre erred embodiment of m improved apparatus shown in the drawing accompanymg and forming a part of this specification. In this drawing, Figure 1 shows, diagrammatically, a complete receiving system cmbodying my improved apparatus and adapted for use in practising my improved method. Fig. 1 shows diagrammaticallv a ortion of the receivin system in modified mm. Fig. 2 is a sectional view of an alternating current generator suitable for use in practisin my invention and Fig. 3 is a ilretaii modi cation of the arrangement of Referring in detail to the arrangement shown in Fig, 1 of the drawing, the numeral 1 designates an antenna grounded at 4 and having a variable inductance, 2, and a vari able ca acity, 3, inserted therein. By suitabl a usting the inductance 2 and ca acity 3 t e eriod of the open circuit may e increases or decreased within the desired limits, it of course being understood that the condenser 3 is only essential when it is desired to increase the natural frequency of the .circuit above the limit, which may be reached by varying the inductance 2. The numeral 5 designates a second variable inductance which also constitutes the secondary of the oscillation transformer formed b the two inductances, 2 and 5. A variable condenser 6 is connected in series with the variable inductance 5 and by suitably adjusting either the inductance 5 or condenser 6 or both the natural period of the closed circuit can be varied and brought into resonance with the open circuit and with the received waves. A rectifying detector, 7, and a condenser, 8, are connected in series with each otlierand in shunt to the inductance 5 and condenser 6. The detector 7 is preferably of a type which requires no batteries for its operation and the condenser 8 is preferably fixed and of such value as to operate best with the particular generator with which it is used. The fields, 9, of an alternating current generator, are connected with the terminals of the condenser 8 so that when the condenser 8 is subjected to difierences of potential, current will flow through the field 9. The currentin the closed circuit formed by inductance 5 and condenser 6 is oscillatory and the function of the detector 7 is to rectify these oscillating currents and make them unidirectional and to cause the unidirectional current to fiow'through the fields 9. The armature coils, 10, correspond in number to the field coils and are connected to the collector rings, 11. The numeral 12 designates the brushes, and the condenser 13 and the telephone or receiving device are connected in series with each other and to these brushes. The condenser 13 is of such value as to neutralize the reactance which would normally be present in the circuit containin the armature and telephone or receiving evice. The generator used must be of special construction and should preferably be constructed without iron and if iron 1s used it should be finally divided or laminated in such a manner that the losses will be reduced to a minimum. The preferred arrangement of the generator is shown in Fig. 2 in which 15 is the field coils, 16 the armature coils, 17 the armature shaft carrying the disk 18 of insulating material employed to support the coils 16.

Any suitable transmitting apparatus may be used in conjunction with the receiving apparatus above described. It is especial y adapted, however, for use with transmitting apparatus adapted to radiate undamped waves or damped waves of a high group frequency.

The operation of my improved apparatus, when employed to ractice my nnproved method, briefly described, is as follows: The oscillations set up in the closed circuit 5, 6 by the waves impinging on the antenna 1, are rectified by the detector 7, and a unidirectional current is caused to flow through the field coils 9. The condenser 8 serves to make this unidirectional current substantially continuous during the entire time the sending key at the transmitting station is closed. And this is true when the oscillations are damped but of a high group frequency as well as when they are continuous or undamped. This current energizes the field coils which in turn energize the armature coils and alternating current is caused to flow through the telephone R. It is understood that the telephone R has a natural frequency and responds with maximum effect to current of that frequency, and that the generator is driven at a speed to produce current havin the same frequency. The frequency oft e generated current is therefore dependent upon the natural freuency of the telephone, and is independent of all frequency or time characteristics of the received oscillations. By the term frequency characteristics I mean both the wave and the roup frequency of damped oscillations and of undamped oscillations which are broken up into groups as well as the wave frequency of the continuous undamped oscillations.

\Vhile the receiving apparatus above described is particularly adapted to receive undamped waves, or waves having a group frequency higher than the frequency of the telephone or even audibility, it may also be used to advantage in cases where the wave trains have the desired audible frequency. In the latter case see Fig. 1 the current can be allowed to fluctuate through the fields 9" with the wave train frequency and a direct current armature 10 may be used instead of an alternating current armature. In this case the frequency of the signal in the telephone will be the same as the wave train frequency, but the E. M. F. will be boosted or increased by the rotation of the armature, and the amount of thisboosting will depend on the speed of the armature within certain limits.

While my invention has special advantages when used in connection with a telephone as a receiving device, yet it will be understood that other receiving devices may be employed with considerable advantage, and while I have only described one embodiment of my improved apparatus and the preferred way of using my improv method, I am aware that modifications may be made by those skilled in the art without departing from the scope of m invention. As an instance of such modi cations the condenser 8 may be omitted and the field coils 9 may be connected across the detector 7 by the leads 19 and 20, as shown in Fig. 3, though this arrangement is not considered so good as'that of Fig. 1.

What I claim is:

1. In an apparatus of the kind described, means for receiving and rectifying continuous undamped oscillations, a generator, the fields of which are arranged so as to be excited by the rectified oscillations, and a receiving device operated by the current from the armature of said generator.

2. In an apparatus of the kind described, means for receivin oscillations, a generator, the fields of w ich are arranged so as to be excited by the rectified oscillations,

and a receiving device operated by the current from the armature of said generator, the frequency of said current being independent of all frequency characteristics of the received oscillations.

3. In an apparatus of the kind described, means for receiving and rectifying oscillations, a generator, the fields of which are arranged so as to be excited by the rectified oscillations, and a receiving device operated by the current from the armature of said generator, said current being of a different frequency than the group frequency of the received oscillations.

4. In an apparatus of the kind described, means for receiving and rectifying continuous undamped oscillations, a telephone adapted to respond with maximum efiect to current having a definite frequency, an alternating current generator havin a frequency corresponding to that of t e telephone, and means for energizing the field coils of said generator by the received rectified oscillations.

5. In an apparatus of the kind described, means for receiving and rectifying oscillations, a telephone adapted to respond with maximum eflect to current having a definite frequency, differing from the group frequency of the received oscillations, an alternating current generator having a frequency corresponding to that of the telephone, and means for energizing the field coils of said generator by the received rectified oscillations.

6. In an apparatus of the kind described, means for receiving and rectifying oscillations, a telephone adapted to respond with maximum effect to current having a definite frequency independent of all frequency characteristics ofthe received oscillations, an alternating current generator having a frequency corresponding to that of the telephone, and means for energizing the field coils of said generator by the received rectified oscillations.

7. In an apparatus of the kind described, means for receiving and rectifying continuous undamped oscillations, a receiving device adapted to respond with maximum effect to current pulses of a particular frequency, an alternating current enerator adapted to produce current of a requency corresponding to that of the receiving device, and means for energizing the field coils by rectified oscillations, for the purpose described.

8. In an apparatusof the kind described, means for receiving and rectifying oscillations, :1 receiving device adapted to respond with maximum effect to current pulses of a particular frequency, diflering from the grou frequency of the received oscillations, an alternating current generator adapted to produce current of a frequency corresponding to that of the receivin device, and means for energizing the fiel cells by the rectified oscillations, for the purpose described.

9. In an apparatus of the kind described, means for receiving and rectifying continuous undamped oscillations, a generator, the field coils of which are arranged to be energized by the rectified oscillations, a com denser in shunt with said coils, and a receiving device connected across the armature coils for the purpose described.

10. In an apparatus of the kind described, means for receiving and rectifying oscillations, a generator, the field coils of which are arranged to be energized by the rectified oscillations, a condenser in shunt with said coils, and a receiving device connected across the armature coils and adapted to respond to a current having a frequency differing from the group frequency of the received oscillations.

11. In an apparatus of the kind described, means for receiving and rectifying oscillations, a' generator, the field coils of which are arranged to be energized by the rectified oscillations, a receivi .-device connected. across the armature coi s of said generator, and adapted to respond to a current having a frequency differing from the group frequency of the received oscillations, and a condenser in series with said receiving device, for the purpose described.

12. In an apparatus of the ln'nd described, means for receiving and rectifyin oscillations, a generator, the fields of w ich are arranged so as to be excited by the rectified oscillations, and a receiving device operated bv current from the armature of said generator, the armature being adapted to be rotated at such a speed as to generate a current of a frequency less than the group frequency of the received oscillations.

13. In an apparatus of the kind described,

means for receiving and rectifying oscillations, a tale hone adapted to respond with maximum e ect to current having a definite frequency lower than the group frequency of the received oscillations, an alternating current nerator having a frequency correspondmg to that of the telephone and means for energizing the field coils of said generator by the received rectified oscillations of a higher frequency.

14. In an apparatus of the kind described, means for receiving and rectifying oscillations, a receiving device adapted to respond with maximum eflect to current pulses of a particular frequency lower than the group frequency of the received oscillations, an alternating current generator adapted to produce current of a frequency equal to that to which the receiving devices respond with maximum efi'ect and means for energizing the field coils by the rectified oscillations for the purpose described.

15. In apparatus of the kind described, means for receiving and rectifying oscillations,-a generator, the field coils of which are arranged to be energized by the rectified oscillations, a condenser in shunt with said coils, and a receiving device connected across the armature coils, the armature being adapted to be rotated at such a speed as to generate a current of a frequency lower than the group frequency of the receiving oscillations.

16. The improvement in methods for receiving radio signals which consists in rectifying the received oscillations and in transforming the rectified current into sinusoidal alternating current of a frequenc best suited for use with the receiving device employed and lower than the group frequency of the received oscillations.

17. The improvement in methods of receiving radio signals, which consists in rectifying the received oscillations and in employing the rectified current to control the operation of a generator of alternating current of a frequency lower than the group frequency of the recelved oscillations.

18. The improvement in methods for transmitting. and receiving radio signals I which consists in transmitting signals by means of oscillations havi a. relatively hi h group frequency, in receiving and rectiing the oscillations and in transforming the rectified current into sinusoidal alter- I natlng current of a comparatively low frequency.

19. The improvement in methods of receiving continuous undamped oscillations, which'consists in rectifying the received I oscillations and in employing the rectified current to control the operation of a generator of alternating current of a desired frequency.

20. The improvement in methods of re- 1 ceiving continuous undamped oscillations, which consists in rectifying the received oscillations and in employing the rectified current to control the operation of a generator of alternating current, of a frequency differing from that of the received oscillations.

21. The improvement in methods of receiving oscillations which consists in rec- 10 tifying the received oscillations and in employing the rectified current to control the operation of a generator of alternating current of a frequency which is independent of all frequency characteristics of the received oscillations.

WALTER S. JONES, WM. M. EnnL. 

